Circular single or multineedle bed knitting machine



NQV. 16, 1954 LAFEUILLADE CIRCULAR SINGLE OR MULTINEEDLE BED KNITTINGMACHINE Y Filed April 26, 1952 3 Sheets-Sheet l .ZA VEA/TOR A MwcaLAFEUILLADE L.

ATTO/F/VE) N m, 1954 M. LAFEUILLADE 2,694,305

CIRCULAR SINGLE OR MULTINEEDLE BED KNITTING MACHINE Filed April 26, 19523 Sheets-Sheet 2 Z/VVf/WUK I MMCEL ZAFEU/LLADE Nov. 16, 1954 LAFEUILLADECIRCULAR SINGLE OR MULTINEEDLE BED KNITTING MACHINE Filed April 26, 19523 Sheets-Sheet 3 5 mw m u y v w E y F 1 m K m M A W k B J 2,694,305Patented Nov. 16, 1954 CIRCULAR SINGLE .OR MULTINEEDLE BED KNITTINGMACHINE Marcel Lafeuillade, Troyes, France, assi'gnor to RaymondeLebocey, Jacqueline H. J. Couste, Annick L. S. Lebocey and Bernard J. E.Lebocey, all of Troyes (Aube), France ApplicationApril 26, 1952,'SerialNo. 284,491 Claims priority, appiication France April 27, 1951 8 6Claims. (CL: 66;-157) My invention is concerned with up-to-datehigh-efficiency knitting machines.

Its object consists in a number of electro-mec hanical devices which asa whole constitute something like a complete system for making theactuating members subject to the various safety apparatus as well ascontrollable at the operators will.

These improvements, which may be; applied separately or in any suitablecombination, may be enumerated as follows:

(A) A self-tripping interlocking mechanism providing for the control ofthe brake as well as forthe making and breaking of the various supplyand safety circuits.

(B) A remote control system including multiple stations favorablydistributed over the 'periphery' of the machine and combined with theaforementioned member for the purpose of conveniently making theoperation dependent on the operators will.

(C) An electro-uncoupler providing for the instantaneous disengagementof the coupling pawl and fed for that purpose with an energizing currentcontrolled by one or several electronic relays responsive to the varioussafety apparatus.

(D) Means fordetecting holes, loose stitches, and so on, adapted toactuate the electro-uncoupling mechanism through the medium of anelectronic circuit balanced by means of a pair of photoelectric cellssuitably arranged in such a manner that the said balance will be upsetas soon as a defect in the knitwork appears in'thefield which eithercell has to take care of.

(E) A way of combining'the various safety appliances with their controlcircuits arranged according to the invention with a view to. meeting allthe eventualities capable of allowing the machine being set intooperation or of causing the set to stop instantaneously.

On most knitting frames various safety appliances are provided whichareadapted upon the occurrence of such an accident as the breakage ofthethread, or of needles, or adefect in the knitwork, to automaticallybring the frame to a standstill.

These detectors involve the use of either purely mechanical means or ofelectro-mechanical combinations capable of stopping the frame as earlyas possible.

Now, in up-to-date circular knitting frames which are rotated at aconsiderable speed, the time-available to practically bring the machineto a standstill is scarcely less than one tenth ofaisecond.

The consequence is that the various solutions proposed up to the presentto automatically stop the machine will no longer satisfy the newrequirements of the problem.

The causes of such a failure are. multiple. Theyare ascribable notablyto the. sluggishness of the relays and electromechanisms and to failuresof the contacts and feelers by which they are actuated. I v Moreover,some major defects practically escape all known detecting systems.Suchare loose stitches and tiny holes which for want of anything betterhad to be left to the care of the operator.

On the other hand, as soon as the machine has-thus been'stopped by suchasafety appliance, the'man in charge of theframe has to ascertain thecauses of the failure, to correct said cause, to re-set the?appliance-ready and to set the frame againinto operation.

Consequently, it became essential not only-.to resort to additionalultra-sensitive;;dete ctingrelays,, but also as much as possible tofacilitate the-intricate operations attending. the watching at theworkand the operation. of

rarne.

.Our t invention. willbe described hereinafter for the purpose ofexemplificationand not; bymeans ofv limita- =tion,.reference beinghad tothe appended drawings.

' Figure 1 is a diagrammatical view which showsthe Iwayi in-Which thevarious subjection and control means mayadvantageously be. arranged andcombined.

,view; of certain d Figure 2is a partial view which more particularlyshows the explanatory diagram of theinterlocking mechanism combined withits remote control means.

Figures 3 and 4. are partial views, in vertical sectional etails ofdesign belonging to the mechanism represented in plan view in Fig. 2.

Figure 5 isan explanatory diagram which diagram- ,maticallyshows anembodiment of the electroniccircuits responsive to therupture of thethread and to the occurrence of a hole respectivelyv and; adapted tocontrol the ,operation of the electro-uncoupler, through the medium of atube relay of the thyratron type. v As shown in Figs. 2 3 and 4asuitably supported and guided chain 1 is arranged below the main disc ofthe frame 2.- Said chain meshes with sprockets 3, 4 keyed on shafts 5, 6extending in a hand lever 7.

Each hand lever7 may assume four particular positions A-B--CD which;respectively correspond to the Stop, Slow running, Brake resetting andQuick 3 the; sector running positions.

} The chain 1 moreover meshes with a toothed sector ;8 keyed on asleeve9 and forming a brake-actuating member.

,Attached to, said slceve 9 is a brake band 10 the other end of which issecured toafixed point 11. The band a 10 is trained about the brake drum12 which is rigid with the maindriving, shaft A of fthemachine 13.

A driving pawl 14, mounted onthe pin 15 rigidwith 7 Scan engage belowthe tooth 17 ofratchet 18 rigid with sleeve A,stop pawl 19 mounted on afixed pin 20 engages in due time thetooth 2110f a second ratchet 22likewise rigid with the sleeve 9.

The ratchet pair 18 and 22 which are rigid with the sleeve 9 are mountedloosely as a whole on the fixed pin hand lever 7 is 23.- By the actionof the spring 24 attached at either to sleeve 9 and to the fixed point25 the ratchets are end urged to rotate counterclockwise.

Such a rotation is only possible when. pawl 19 is disengaged from tooth21.

In other terms, the spring the brake-actuating member position in whichit operates the brake formed by the band 10 and the drum 12. The pawl 19and ratchet 22 act as a locking-catch for retaining the brake actuatingmember 8 in a cocked and inoperativeposition. The disengagement of pawl19 is controlled in due time by theuncoupling electromagnet 26 actingupon the movable armature constituted by thetail 19a of pawl 19.

The relative position of the interlocking members indicated by the Figs.1 and Zis the oneobtained when the brought to the so-called Brakeresetting posit on C. In this position: i

(a) The, band 10 isreleased without an action upon the drum 12.

(b) The ratchet 22 engaged onpawl 9 is not respon- 24 is adapted forurging .8 towards and up to the sive to spring 24.

(c) The boss 27, cut in ratchet 18 acts upon the push -roll 28 toshort-circuit the terminals 29 :and 30 of the various-:control circuits.

-(d) The push rolls 32 and 33 of the conventionalpat- -tern, urged bytheir springs, respectively short-circuit the terminals 34 '-35" and3637' belonging to determined circuits the functions of which will beexplained hereinafter.

ing of the transformer 31 which thr ou ghits secondary supply wireswhich lead .to the. cut-off switch 45.

As soon as said cut-off switch is switched in: -(a) The terminals 46.and 47 feed the primary. windterminals 48-49 provides for the heating ofthe filament in the tube relay R.

(b) The terminals 47 and 50 of the feed line are live, yet theconnection circuit cannot be established as long as the pair of starters51 and 52 are still open.

The operation of the said starters has been described in the U. S.application Ser. No. 257,248, filed November 20, 1951, by BernardLebocey.

The two said starters constitute a safety appliance inasmuch as theywill delay by a few seconds the contingent establishment of the currentin the driving circuits. This mere precaution practically prevents thestarting of the frame into operation before the thyratron relay R, onceduly heated, is capable of performing its function.

As soon as the ionization process has closed the starters 51 and 52 thecut-off switch is thrown in automatically.

(d) The Slow-running motor fed through the three wires 54, 55, 56remains stopped since the circuit for the energization of its automaticcut-off switch 57 which is fed through the terminals 58-59 oftransformer 31 remains open at the terminals 40 and 41 of the push roll33.

e) The quick running motor fed through the three wires 60-6162 remainsat rest since the circuit adapted to energize its cut-off switch 63,which is likewise fed from the terminals 58-59, is cut off at theterminals 38-39 of the push roll 32.

In order that the frame can be started through the medium of theSlow-running motor it is necessary to shift the hand lever 7 from C toB. In this position:

(a) The chain 1 which has moved towards the left and has driven thesector 8 of which the stop 64 has thrust the push roll 33 in such amanner that the two terminals 40 and 41 are now short-circuited whilethe circuit 3637 has been cut off.

(b) The current tapped at the terminals 5859 of the transformer 31 hasclosed through the points 59- 65-66-404167-68-37-30--29-58 on theenergizing coil of the automatic cut-off switch 57, and this, oncondition that contacts 6768 are closed.

(c) The closing of contacts 67-68 is controlled advantageously by meansof safety appliances known by thenames of clogging detectors and brokenneedle detectors connected in series with the line.

In normal position the said detectors close the contacts.

Conversely, has become inoperative, ously the frame cannot be set againinto operation until the detector concerned has been re-set.

(d) As soon as the hand lever brought to position B is released thespring assigned to push roll 33 by acting as soon as any one of saiddetectors upon sector 8 through stop 64 will become effective to h movethe sector back to the right in such a manner that the saidv hand leverwill assume its normal position at A. The frame is stopped since thecircuit is cut oflf at 4041.

In order to start the frame into quick-running operation it is necessaryto shift the hand lever 7 to D-position.

In the said position:

(a) The chain 1 which has moved towards the right has swung the sector 8in such a manner that its stop 69 by engaging the push roll 32 hasthrust the latter to establish contact at 38-39 while temporarilybreaking the safctycircuit leading to terminals 34-35.

(b) The current tapped at the terminals 58-59 of the transformer.31 willthen close through the winding designed to energize the automaticcut-off switch 63 provided the contacts 67-68 are closed, which involvesthat all the contact-controlling detectors are set.

The circuit for the maintenance of the quick operation automatic cut-offswitch 63 is thus established through points 58-29-303736-666559.

(c) In the course of such a swinging motion the sector 8 has also movedthe pawl 14 the tail 14a of which has come into engagement with thefixed stop 70 in such a manner that said pawl 14 has disengaged tooth17, whereby ratchet 18 has been released quite temporarily.

The consequence of such an arrangement is that whenever theelectromagnet 26 is operated and thereby becomes effective to attractpawl 19 and release the interlocking mechanism the spring 24 will rotatethe sleeve the circuit is broken and obvi- 9 providing the locking ofthe brake by the tension of the band 10.

On the other hand the ratchet 18 rigid with ratchet 22 will rotatetherewith. The boss 27 will cease to act upon the push roll 28 whichinstantaneously will cut off the circuit leading to the terminals 29 and30.

As a consequence of the cutting off of the holding circuit for theautomatic cut-off switch 63 the quick running motor will be stoppedinstantaneously.

Consequently, it will only be necessary to energize theelectro-uncoupler 26 to cut off the supply to the "quick running motorand simultaneously causing the automatic release of the brake.

The energization of the electromagnet 26 may be controlled by the wholeor part of the various safety appliances.

With this end in view, the aforementioned arrangement may advantageouslybe combined with the so-called electronic thread-rupture detectorproviding the subject-matter of the aforementioned application.

The same arrangement may also be combined with electronic means adaptedto detect holes or loose stitches.

According to the invention, an embodiment of such a combination will bedescribed hereinafter by way of example, reference being had to Figs. 1and 5 of the appended drawings:

The feed of the electro-uncoupler 26 is ensured from the secondaryterminals 071 of the transformer 72, the circuit being operated througha tube of the thyratron" type R the heating of the filament of which isensured previously through the transformer 31 as indicated precedingly.

According to an improvement of the invention according to thearrangement provided in the aforementioned application the feed of thegrid potential may be effected crosswise to the potential 73 and of therectifier 74 from the pair of terminals 75 and 76 of the filamentheating circuit.

It will be recalled that the accidental fall of the detector tumblingarm 77 which normally is kept in its raised position by the thread 78has for its effect to earth the antenna 79, a circumstance which issufficient to destroy the normal grid-biasing potential. Thecathode-anode circuit will then be established in the relay R and theelectro-magnet 26 releases the brake and stops the machine.

This arrangement may moreover be combined with the electronic hole andloose-stitch detector."

The said electronic detector is intended to stop the frame as soon as adefective place in the web (holes, loose stitches, and so on) appears inthe field assigned to one or several photoelectric cells.

According to a new example of achievement and application which will bedescribed hereinafter, reference being had to the Figs. 1 and 5, a pairof suitably directed and supported photoelectric cells 80 and 81permanently scan two different areas of the periphery of the knitworkweb N, which web assumes the shape of a practically cylindrical tubewhich is comparatively transparent as it leaves the needles. One orseveral projection lamps 82 favorably arranged within said tubular webemit light bundles capable of influencing the two sensitive cellsthrough the knitwork.

The two cells are fed through the secondary terminals 83 and 84 arrangedat either side of the terminal 0 which is earthed.

The two cells 80 and 81 are in series in the circuit, their connectionbeing established in the cathode-anode direction from terminal 83.

A point P, taken in the circuit, between the anode of cell 80 and thecathode of cell 81 is connected withthe grid of the thyratron tube R.

In normal Working, it may be admitted that the relative transparency ofweb N, considered at the same time in the scanning field of the twocells remains substantially the same. The two cells collect each a lightflux of equal intensity, their'internal resistances are, at that verytive relative to point 0. I

positive, whereas that of terminal 83 at that time is nega-Consequently, it is always possible to choose the conditions ofbalancing of points 83 and 84 in'such a. manner that the potential of Pwill always assume a negative value which in its absolute value ishigher than or equal to the one necessary to cause the thyratron grid toprevent the priming of the relay, and this, in normal workingconditions.

It being assumed that a hole or a loose stitch appears accidentally inthe field of cell 80, whereby the light flux striking the cathode isincreased, it is evident that the internal resistance of said cell willdecrease, thus creating a disequilibrium which will be translated into avariation in the potential of P, which will become closer to thenegative potential of the terminal 83, thus aggravating the grid lockingconditions.

Quite the contrary, as soon as the aforesaid hole appears in the fieldof cell 81, the same process will go on except that since the potentialof P becomes closer to that of the positive terminal 84 it will beenabled to assume a positive value which is sutficient to set the relayout of balance, and thereby to initiate the energization of theelectro-uncoupler 26 by which the frame will be. stoppedinstantaneously.

However, the conditions of utilization of such a device require certaincomplementary arrangements.

Effectively, as soon as the uncoupler has functioned, the operator mustbe enabled to take the defective place. out of the field of the cellconcerned and to start the frame into operation again.

With this end in view, the cell feed circuit is provided with a cut-offat the terminals 34-35 which in normal working conditions areshort-circuited by the push 32.

Consequently, it is only necessary for the operator to swing the handlever 7 back from A to C to keep said lever a few seconds in the.last-mentioned position, as a result of which the frame is re-startedinto Quick-running operation while the said circuit will be cut off forsufficient time to allow the defective place to move away before thesafety circuit considered is re-establishcd.

On the other hand, it may prove desirable to provide for a complementarysafety device intended to become ef-. fective in the event the thyratronrelay should happen to fail. 1 a

With this end in view, an auxiliary relay 85 is provided the operationof which is as follows:

As soon. as the thread happens to fall with the feelers arm theelectronic frame stop comes into action. If the latter in its turnhappens to fail, e. g. consequent to the thyratron tube getting out oforder, thread will begin to clog the needle hooks, as a consequence ofwhich the clogging detector are moved upwards and thereby proi-J'.

vide for the opening of the aforesaid contacts 67--68.

At that moment the relay 85 which is no longer energized will releaseits movable armature 86 by which the terminals 87 and 88 areshort-circuited.

The circuit is then closed to earth between the terminals and 71 and thecoil 26 mounted in series in the same circuit will bring the frame to astandstill.

What I claim is:

1. In a circular knitting machine having a plurality of motorcontrol-and-safety circuits, a control device comprising a brake adaptedto stop the working of the machine, a brake-actuating member for saidbrake, a spring adapted for urging said brake-actuating member towardand up to its operative position, a locking catch for retaining saidbrake-actuating member in a cocked and inoperative position against thestress of the spring, circuit control means operatively associated withsaid brakeactuating member for timely operating the motorcontrol-and-safety-circuits of the machine, at least one commonhand-operated member having a driving connection with saidbrake-actuating member, and thereby adapted for shifting back saidbrake-actuating member from its operative to its cocked and inoperativeposition against the stress of the spring, said hand operated memberbeing lockable in several difierent positions in which the circuitcontrol means operatively associated with the brake-actuating member setin operation different motor control-and-safety-circuits, anelectromagnet having its armature connected to the aforesaid lockingcatch, and means responsive to the defects in operation of the knittingmachine, adapted for electric action sults in the release of the;brake:ac., ating--member up, to

its operative position andyin the timelypperation of the different motorcontrol-and:safety-circuits of the machine. r .1

2. In a circular knitting'machine having 'a plurality of motorandsafety-circuitsamong-which are a slow running motor-circuit and'aquick-running motor-circuit, a control device comprising a brake;adapted to stop the working of the machine, a 'brakfi, actuating memberfor said brake, a spring adapted forurgingfsaid brake actnating membertoward and up to .its-operati ve position, a locking catch for retainingsaid brake-actuating member in a cocked and inoperative position againstthe stress of the spring, circuit control-meansoperatively -a'ssocia'ted with said brake-actuating member-for timely operating the motorandsafety-circuits-of'the'machine, at least one common hand-operatedmernberhaving a'driv ingconnection with said brake-actuating=mernber,and thereby adapted for shifting back said;;brake actuating memberfrom its operative to its cocked and inoperative, position against thestress of the spring, said hand-operated member being lockable in'several different positions .in which the circuit-control meansoperatively-associated with the brake-actuating member set in operationdifferent motorand safety-circuits and among whichv are a slow runningmotor-circuit position and, a quickrunningmotor-circuit position, anelectromagnet'having its armature connected to the aforesaid lockingcatch, and means responsive to the defects in operation of the knittingmachine, adapted for electric action upon the energizing circuit of saidelectromagnet and for consequent unlocking of said locking catch, whichresults in the release of-.- the brake-actuating member up to itsoperative position and in the timely operation of the different motorandsafetycircuits of the machine, a

3. In a circular knitting machine-having a plurality of motor control:and safety circuits, a control device comprising a brake adapted totstop the working ofthe machine, a brake-actuating member for' saidjbrake, a spring adapted for urging said brake-actuating member towardand up to its operative position, a; locking catch for retaining saidbrake-actuating member in a cocked and inoperative position against,thestress of the spring, circuit control means operativelyassociatedwith said brake-actuating member fortim'ely; operating the motorcontroland safetyvcircuits .of .the machine, at least one commonhand-operated memberhaving a driving connection with saidbrake-actuatingmember,,and thereby adapted for shifting back saidbrake-actuating member from its operative to its cocked and-inoperativeposition against the stress of the spring, said hand-operated memberbeing lockable in several'ditferent positions in which the circuitcontrol means operatively associated with the brake-actuating member setin operation different motor controland safety-circuits, anelectromagnet having its armature connected to the aforesaid lockingcatch, a thyratron tube having its cathode-anode circuit connected tothe energizing circuit of said electromagnet, and means responsive tothe defects in operation of the knitting machine, adapted for electricaction upon at least one grid of said thyratron tube and for consequentunlocking of the locking catch connected to the annature of theelectromagnet, which results in the releas of the brake-actuating memberup to its operative position and in the timely operation of thedifferent motor and safety-circuits of the machine.

4. In a circular knitting machine having a plurality of motor controlandsafety-circuits, a control device comprising a brake adapted to stop theworking of the machine, a brake-actuating member for said brake, aspring adapted for urging said brake-actuating member toward.

and up to its operative position, a locking catch for retaining saidbrake-actuating member in a cocked and inoperative position against thestress of the spring, circuit control means operatively associated withsaid brakeactuating member for timely operating the motor controlandsafety-circuits of the machine, at least one common hand-operated memberhaving a driving connection with said brake-actuating member, andthereby adapted for shifting back said brake-actuating member from itsoperative to its cocked and inoperative position against the stress ofthe spring, said hand-operated member being lockable in severaldifferent positions in which the circuit control means operativelyassociated with the brakeactuating member set in operation differentmotor controland safety-circuits, an elctromagnet having its armatureconnected to the aforesaid locking catch, a thyratron tube having itscathode-anode circuit connected to the energizing circuit of saidelectromagnet, and a thread rupture responsive detector adapted forelectric action upon a grid of said thyratron tube and for consequentunlocking of the locking catch connected to the armature of theelectromagnet, which results in the release of the brake-actuatingmember up to its operative position and indie timely operation of thedifferent motorand safetycircuits of the machine.

5. In a circular knitting machine having a plurality of motorcontrolandsafety-circuits, a control device comprising a'brake adaptedto stop the working of the machine, a brake-actuating member for saidbrake, a spring adapted for urging said brake-actuating member towardand up to its operative position, a locking catch for retaining saidbrake-actuating member in a cocked and inoperative position against thestress of the spring, circuit control means operatively associated withsaid brakeactuating member for timely operating the motor controlandsafety-circuits of the machine, at least one common hand-operated memberhaving a driving connection with said brake-actuating member, andthereby adapted for shifting back said brake-actuating member from itsoperative to its cocked and inoperative position against the stress ofthe spring, said hand-operated member being lockable in severaldifferent positions in which the circuit control means operativelyassociated with the brake-actuating member set in operation differentmotor controland safety-circuits, an electromagnet having its armatureconnected to the aforesaid locking catch, a thyratron tube having itscathode-anode circuit connected to the energizing circuit of saidelectromagnet, a pair of photoelectric cells having their scanning fielddirected upon two different areas of the periphery of the knit-work ofthe circular knitting machine and electrically connected fordifferential action upon a grid of the thyratron tube, thereby adaptedto produce an electric action upon the energizing circuit of theelectromagnet and consequently to stop the machine whenever a defectappears in the scanning field of one of the cells.

6. In a circular knitting machine having a plurality of motor controlandsafety-circuits, a control device comprising a brake adapted to stop theworking of the machine, a brake-actuating member for said brake, aspring adapted for urging said brake-actuating member toward and up toits operative position, a locking catch for retaining saidbrake-actuating member in a cocked and inoperative position against thestress of the spring, circuit control means operatively associated withsaid brakeactuating member for timely operating the motor controlandsafety-circuits of the machine, at least one common hand-operated memberhaving a driving connection with said brake-actuating member, andthereby adapted for shifting back said brake-actuating member from itsoperative to its cocked and inoperative position against the stress ofthe spring, said hand-operated member being lockable in severaldifferent positions in which the circuit control means operativelyassociated with the brake-actuating member set in operation differentmotor controland safety-circuits, an electromagnet having its armatureconnected to the aforesaid locking catch, a thyratron tube having itscathode-anode circuit connected to the energizing circuit of saidelectromagnet, a thread rupture responsive detector adapted for electricaction upon a grid of said thyratron tube and for consequent unlockingof the locking catch connected to the armature of the elec tromagnet,which results in the stopping of the machine upon occurrence of a threadrupture, a pair of photoelectric cells having their scanning fielddirected upon two different areas of the periphery of the knit work ofthe circular knitting machine and electrically connected fordifferential action upon a grid of the thyratron tube, thereby adaptedto produce an electric action upon the energizing circuit of theelectromagnet and consequently to stop the machine whenever a defectappears in the scanning field of one of the cells.

7. In a circular knitting machine having a plurality of motor controlandsafety-circuits, a control device as claimed in claim 1, andirreversible clogging-responsive circuit breakers inserted in the motorcontrol-circuits and adapted to cut off the power circuits of the motorswhen set in the breaking position, whereby a hand resetting of saidcircuit breakers to their closed position must be effected prior to anyrestarting of the motors.

8. In a circular knitting machine having a plurality of motor controlandsafety-circuits, a control device as claimed in claim 3, irreversibleclogging-responsive circuit breakers inserted in the motor controlcircuits and adapted to cut off the power circuits of the motors whenset in the breaking position, whereby a hand resetting of said circuitbreakers to their closed position must be effected prior to anyrestarting of the motors, and an auxiliary clogging-responsive relayadapted for direct electric action independent of the thyratron tubeupon the energizing circuit of the aforesaid electromagnet, providingthus a complementary safety device intended to become effective in theevent of failure of the thyratron tube.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,165,975 Lawson July 11, 1939 2,290,257 Stanley et al. July21, 1942 2,346,240 Thomas Apr. ll, 1944 2,564,413 Vossen Aug. 14, 1951FOREIGN PATENTS Number Country Date 455,243 Canada Mar. 15, 1949

